1. Chemistry, School of Engineering and Physical Science, Heriot-Watt University, Edinburgh EH14 4AS, UK
2. Istituto per lo Studio delle Macromolecole, ISMAC-C.N.R, Milano, Italy
3. ISIS, Rutherford Appleton Laboratory, Chilton, Didcot OX11 OQX, UK
4. Istituto Processi Chimico-Fisici, Sezione di Messina-CNR, Messina, Italy